(1) Field of the Invention
The present invention relates to a vibration isolating mount for use with a vibratory pile driver and extractor. In particular, the present invention relates to an improved vibration isolating mount that provides improved isolation of high vibration forces, an increased resistance to failure when the vibration isolating mount is stressed in shear, and provides an increased resistance to deterioration from prolonged exposure to the environment.
(2) Description of the Related Art
Vibratory pile drivers and extractors of the type with which the present invention is employed are generally comprised of four distinct parts. A suspension housing, a plurality of vibration isolating mounts, a vibratory exciter, and a clamp housing. The suspension housing is suspended by a cable from a crane, and is connected to the vibratory exciter by a plurality of vibration isolating mounts. The clamp housing is bolted to the vibratory exciter and is operated by hydraulic pressure to grip the top edge of metal sheeting or the top end of a pile that is to be driven into or pulled from the ground. A typical vibratory exciter of the prior art consists of a housing containing an eccentric that is driven by a hydraulic motor. The hydraulic motor rotates the eccentric and the rotation of the eccentric produces a vibration that causes the entire vibratory exciter and clamp housing assembly to vibrate up and down.
The vibration of the vibratory exciter, secured to the top of the metal sheeting or pile by the clamp housing, transmits a pulsating force to the sheeting or pile. When the vibratory exciter and clamp housing assembly is suspended by the crane cable so that the assembly is essentially just resting on the top of the sheeting or pile, the vibration of the vibratory exciter will produce a pulsating up and down force on the sheeting or pile that will enable the weight of the exciter and clamp housing assembly to drive the sheeting or pile downward into the ground. When employing the exciter and clamp housing assembly as a driver, the isolating mounts connecting the exciter to the suspension housing reduce the vibration to the suspension housing.
It is desirable that virtually no vibration be transmitted to the suspension housing and then through the crane cable to the crane. However, the vibration from the exciter must still be transmitted to the sheeting or pile through the clamp housing.
When employing the vibratory pile driver and extractor to extract metal sheeting or piles from the ground, the vibratory exciter and clamp housing assembly are again positioned on the top edge of the sheeting or the top end of the pile and the clamp is actuated to grip the top of the sheeting or pile. With the clamp gripping the sheeting or pile, and the vibratory exciter motor running, the suspension housing is raised by the crane operator so that the vibration isolating mounts connecting the vibratory exciter to the suspension housing are stretched. The stretched isolating mounts exert an upward pulling force on the vibratory exciter and then to the sheeting or pile through the clamp housing. The origin of this upward pulling force is the amount of force exerted by the crane cable.
Prior art vibration isolating mounts are typically comprised of a large rectangular block of rubber, with a large hole in the center, that is chemically bonded between a pair of metal plates. One plate of the pair is secured to the vibratory exciter and the other is secured to the suspension housing. These isolating mounts were not designed specifically to be used on vibratory pile driver and extractor equipment. They were "Dock Fenders" used for absorbing compression loads of ships docking against loading docks. These mounts have been found to be disadvantaged in that their materials and their construction permit the exertion of only a limited pulling force before they fail in shear stress. Shear stress failure of prior art vibration isolating mounts subjected to a large pulling force occurs when one or both of the metal plates begin to separate from the rubber block or the rubber block itself begins to tear.
The useful life of prior art vibration isolating mounts is also lessened by their prolonged exposure to the outside environment during use. It has been observed that exposure to the environment has a deteriorating effect on the rubber blocks of prior art mounts. The deterioration of the blocks lessens the mounts useful life.
The vibration isolating mount of the present invention overcomes disadvantages associated with prior art mounts by providing a mount of unique construction and design that enhances the ability of the mount to resist shear stress failure. It was designed specifically to solve the problems of the mounts previously being used in the vibratory pile driver and extractor industry. The construction of the mount enables it to sustain a much larger pulling force without failing than was heretofore available with prior art vibration isolating mounts.
The vibration isolating mount of the present invention is very effective in reducing vibration of crane cables in both driving and pulling operations. The pulling operation, particularly the large shear stresses developed by the pulling force required to pull some sheeting or piles from the ground, causes a cross section area of a polyurethane center section of the mount to be reduced considerably as the center section elongates in response to the large pulling force involved. This reduced cross section of the polyurethane center member is very effective in reducing the amount of vibration transmitted to the suspension housing and then to the crane cable.
The unique construction also provides a vibration isolating mount that has significantly less weight than prior art mounts and therefore is easier to manipulate and less expensive to ship than prior art mounts.
The vibration isolating mount of the present invention is also constructed of materials that are more resistant to the deteriorating effects of the environment than are the materials employed in prior art vibration isolating mounts.